Zeolites, both natural and synthetic, have been demonstrated in the past to have catalytic properties for various types of hydrocarbon conversion. Certain zeolitic materials are ordered, porous crystalline aluminosilicates having a definite crystalline structure as determined by X-ray diffraction, within which there are a large number of smaller cavities which may be interconnected by a number of still smaller channels or pores. The pore systems of other zeolites lack cavities, and these systems consist essentially of unidimensional channels which extend throughout the crystal lattice. Since the dimensions of zeolite pores are such as to accept for adsorption molecules of certain dimensions while rejecting those of larger dimensions, these materials are known as "molecular sieves" and are utilized in a variety of ways to take advantage of these properties.
Such molecular sieves, both natural and synthetic, include a wide variety of positive ion-containing crystalline silicates. These silicates can be described as a rigid three-dimensional framework of SiO.sub.4 and, optionally, Periodic Table Group IIIB element oxide, e.g., AlO.sub.4, in which the tetrahedra are cross-linked by the sharing of oxygen atoms whereby the ratio of the total Group IIIB element, e.g., aluminum, and Group IVB element, e.g., silicon, atoms to oxygen atoms is 1:2. The electrovalence of the tetrahedra containing the Group IIIB element, e.g., aluminum, is balanced by the inclusion in the crystal of a cation, for example, an alkali metal or an alkaline earth metal cation. This can be expressed wherein the ratio of the Group IIIB element, e.g., aluminum, to the number of various cations, such as Ca.sup.30 2, Sr.sup.+2, Na.sup.+, K.sup.+, Li.sup.+, is equal to unity. One type of cation may be exchanged either entirely or partially with another type of cation utilizing ion exchange techniques in a conventional manner. By means of such cation exchange, it has been possible to vary the properties of a given silicate by suitable selection of the cation. The spaces between the tetrahedra are occupied by molecules of water prior to dehydration.
Prior art techniques have resulted in the formation of a great variety of synthetic zeolites. Many of these zeolites have come to be designated by letter or other convenient symbols, as illustrated by zeolite A (U.S. Pat. No. 2,882,243); zeolite X (U.S. Pat. No. 2,882,244); zeolite Y (U.S. Pat. No. 3,130,007); zeolite ZK-5 (U.S. Pat. No. 3,247,195); zeolite ZK-4 (U.S. Pat. No. 3,314,752); zeolite ZSM-5 (U.S. Pat. No. 3,702,886); zeolite ZSM-11 (U.S. Pat. 3,709,979); zeolite ZSM-12 (U.S. Pat. 3,832,449); zeolite ZSM-20 (U.S. Pat. No. 3,972,983); ZSM-35 (U.S. Pat. No. 4,016,245); and zeolite ZSM-23 (U.S. Pat. No. 4,076,842), merely to name a few.
The SiO.sub.2 /Al.sub.2 O.sub.3 ratio of a given zeolite is often variable. For example, zeolite X can be synthesized with SiO.sub.2 /Al.sub.2 O.sub.3 ratios of from 2 to 3; zeolite Y, from 3 to about 6. In some zeolites, the upper limit of the SiO.sub.2 /A.sub.2 O.sub.3 ratio is unbounded. ZSM-5 is one such example wherein the SiO.sub.2 /Al.sub.2 O.sub.3 ratio is at least 5 and up to the limits of present analytical measurement techniques. U.S. Pat. No. 3,941,871 (Re. 29,948) discloses a porous crystalline silicate made from a reaction mixture containing no deliberately added alumina in the recipe and exhibiting the X-ray diffraction pattern characteristic of ZSM-5. U.S. Pat. Nos. 4,061,724; 4,073,865 and 4,104,294 describe crystalline silicates of varying alumina and metal content.
Aluminum phosphates are taught in U.S. Pat. Nos. 4,310,440 and 4,385,994, for example. These aluminum phosphate materials have essentially electroneutral lattices. These lattices may be described in terms of alternating AlO.sub.4 and PO.sub.4 tetrahedra. An example of such an aluminum phosphate is a material designated as AlPO.sub.4 -5.
Details of the structure of AlPO.sub.4 -5 are given by Meier and Olson in, Atlas of Zeolite Structure Types, 2nd rev. ed., published on behalf of the Structure Commission of the International Zeolite Association by Butterworths (1987). More particularly, Meier and Olson indicate that AlPO.sub.4 -5, also designated as AFI, is a material having pore windows formed by 12 tetrahedral members, these windows being about 7.3 Angstroms in diameter.
Of the siliceous zeolites discussed hereinabove, zeolites X and Y have the largest pore diameter and overall pore volume. Zeolites X and Y are synthetic analogues of the naturally occurring zeolite, faujasite. Details of the structure of faujasite are also given by Meier and Olson, ibid. More particularly, Meier and Olson indicate that faujasite, also designated as FAU, is a material having pore windows formed by 12 tetrahedral members, these windows being about 7.4 Angstroms in diameter. For the purposes of the present disclosure, the terms, siliceous zeolite and siliceous oxide, are defined as materials wherein at least 50 mole percent of the oxides thereof, as determined by elemental analysis, are silica. The pore volume of faujasite is believed to be about 0.26 cc/g.
An oxide material with even larger pores than faujasite and AlPO.sub.4 -5 is a material designated as VPI-5. The structure of VPI-5 is described by Davis et al in an article entitled, "VPI-5: The first molecular sieve with pores larger than 10 Angstroms", Zeolites, Vol. 8, 362-366 (1988). As indicated by Davies et al, VPI-5 has pore windows formed by 18 tetrahedral members of about 12-13 Angstroms in diameter. A material having the same structure as VPI-5 is designated MCM-9 and is described in U.S. Pat. No. 4,880,611.
A naturally occurring, highly hydrated basic ferric oxyphosphate mineral, cacoxenite, is reported by Moore and Shen, Nature, Vol. 306, No. 5941, 356-358 (1983) to have a framework structure containing very large channels with a calculated free pore diameter of 14.2 Angstroms. R. Szostak et al., Zeolites: Facts, Figures, Future, Elsevier Science Publishers B.V. (1989), present work showing cacoxenite as being very hydrophilic, i.e., adsorbing non-polar hydrocarbons only with great difficulty. Their work also shows that thermal treatment of cacoxenite causes an overall decline in X-ray peak intensity.
In layered materials, the interatomic bonding in two directions of the crystalline lattice is substantially different from that in the third direction, resulting in a structure that contains cohesive units resembling sheets. Usually, the bonding between the atoms within these sheets is highly covalent, while adjacent layers are held together by ionic forces or van der Waals interactions. These latter forces can frequently be neutralized by relatively modest chemical means, while the bonding between atoms within the layers remains intact and unaffected.
Certain layered materials, which contain layers capable of being spaced apart with a swelling agent, may be pillared to provide materials having a large degree of porosity. Examples of such layered materials include clays. Such clays may be swollen with water, whereby the layers of the clay are spaced apart by water molecules. Other layered materials are not swellable with water, but may be swollen with certain organic swelling agents such as amines and quaternary ammonium compounds. Examples of such non-water swellable layered materials are described in U.S. Pat. No. 4,859,648 and include trititanates, perovskites and layered silicates, such as magadiite and kenyaite. Another example of a non-water swellable layered material, which can be swollen with certain organic swelling agents, is a vacancy-containing titanometallate material, as described in U.S. Pat. No. 4,831,006.
Once a layered material is swollen, the material may be pillared by interposing a thermally stable substance, such as silica, between the spaced apart layers. The aforementioned U.S. Pat. Nos. 4,831,006 and 4,859,648 describe methods for pillaring the non-water swellable layered materials described therein and are incorporated herein by reference for definition of pillaring and pillared materials.
Other patents teaching pillaring of layered materials and the pillared products include U.S. Pat. Nos. 4,216,188; 4,248,739; 4,176,090 and 4,367,163; and European Patent Application 205,711.
Whole crude oils contain trace salts, such as NaCl and CaCl.sub.2, and solids, which can cause equipment corrosion/fouling and downstream catalyst deactivation. Consequently, desalting is an important reaction in crude oil refining.
Salts and solids are conventionally removed in a desalting unit by mixing the crude oil with water and de-emulsifying chemicals. As a result of desalting, a significant quantity of waste water that contains salts, solids, benzene and other hydrocarbons is generated. In addition, the desalter generates emulsions which are difficult to break or recover in existing equipment. To meet the Benzene NESHAPS regulation, many refineries are required to remove benzene from the waste water stream generated by the desalting unit. Future regulations may require additional reduction of hydrocarbons.
Salt removal in conventional zeolite pores is restricted by low capacity for salt deposition. Solids generally have a particle size greater than about 1 micron and are also not readily accessible to the surface of conventional zeolite pores.
Therefore, it is an object of the present invention to provide a catalytic desalting process that conserves water. It is a further object of the present invention to provide a catalytic desalting process that minimizes aqueous waste by eliminating the need for water in crude oil desalting.